Synchronized oscillator circuit



April l5, 1952 J. E. BRIDGES SYNCHRONZED OSCILLATOR CIRCUIT 3 Sheets-Sheet l Filed NOV. l0, 1949 Saggi d Ul D S 3 oom u l. O l, n m.. 1. Q com U8..

April 15, 1952 J. E. BRIDGES SYNCHRONIZED OSCILLATOR CIRCUIT 3 Sheets-Sheet 2 Filed NOV. l0, 1949 JACK E. BRIDGES INVEN TOR.

HI S ATTORNEY lDllUalOd l 2.52m o m, .Sl d No w om |m m .Q m23. wem 63.25 O AImEE.

April l5, 1952 J. E. BRIDGES 2,593,005

SYNCHRONIZED OSCILLATOR CIRCUIT Filed Nov. 10, 1949 3 Sheets-Sheet 5 JACK E. BRIDGES r-ll'- INVENToR.

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HIS ATTORNEY Patented Apr. 15, 1952 SYNCHRONIZED OSCILLATOR CIRCUIT Jack E. Bridges, Cicero, Ill., assignor to Zenith Radio Corporationya corporation of Illinois Application ll\love rrlber 10, 1949, Serial No. 126,600

6 Claims. l

This invention relates to oscillator circuits adapted to be synchronized with incoming synchronizing pulses or with an intermittent-series of Vsuch pulses.

This invention nds ready application to-a television receiver wherein it may be used to generate a deflectionsignal for controlling the sweep Vof the cathode-ray reproducing device `utilized in such receivers, the frequency of this deflection signal being synchronized with receivedsynchronizing signals. However, the invention isvalso useful 'in a variety of other electrical systems. For example, the oscillator of the present invention may be used as a -frequency multiplier, vand as such will generate Va signal synchronized-with received synchronizing pulses, but having `a `frequency that is'some `multiple of the' repetition frequency of the pulses.

To overcome the deleterious effects of noise disturbances and other-interferingsignalslon the scanning process of a Atelevision receiver, synchronizing `systems for such receivers'have been proposed that have 4some immunity to these disturbances. The chief 4 disadvantage of these prior art synchronizing systems is that they are *highly complicated and involve a large number `of component stages. One prior system, -for example, requires three distinct stages, namely aphase ldetector, a reactance-tube circuit, and an'oscillator.

Received synchronizing pulses are compared lin the phase detector circuit with the output signal of the oscillator to produce a control signal. lThe control signal is applied to the reactance-tube circuit'which, in turn, controls `thel frequency of the oscillator to maintain synchronism between its output signal and the received synchronizing pulses. This synchronized outputsignal is then utilized to control thersweep of the image reproducing tube.

VThe .present invention provides an oscillator circuit that may be utilized to generate an'output signal for controlling the scanning process of a 'television receiver, and this oscillator circuit has the feature that it may be readily synchronized with received synchronizing pulses withoutjthe need for separate phase detector, re-

actance-,tube 'and otherstages.

It is, accordingly, 4an object of this'invention A to provide, an'improved oscillator circuit that may vide an improved system for controlling thescanning process of a television receiver .that is leX- Vtremely accurate and reliable in operation Aand yet uses a minimum of circuit elements and stages.V

The vfeatures of this invention which are believed to be new are set forth with particularity in the appended claims. The invention itself. however, `together with further objects and -advantages thereof may best be understood by -reference to the following description when'taken in conjunction with the accompanying drawings, in which:

Figure 1 illustrates the Voscillator circuit -of the invention in block form,

Figures 2-6 comprise various diagrams -useful in understanding the invention,

Figure "7 represents -a television receiver incorporating the invention,

4Figure V8 is a schematic diagram of one Vernbodiment of the invention,

Figure 9 is a schematic diagram of a second embodiment of the invention, and

Figures 10 and 11 are vector diagrams useful jin understanding the circuit of Figure 9.

The circuit of Figure l comprises a pair of 'low mu electron-discharge devices I0 and `II which may be conveniently combined as a double triode in a single envelope. The cathode I2 of device I0 is connected to ground and the cathodeIS of device I I is similarly connected to ground. The anode I4 Aof device I Dis connected to one input terminal of a unit I5 and the anode I6 of device I I is connected to a further input terminal of this unit. The circuitry of unit I5 is to be described Yin detail hereinafter, it is deemed suicientat this point to state that this unit Vserves a dual purpose: firstly as an anode load impedance for deriving a push-pull output signal from the devices I0, II; and secondly as a phase-shift network for controlling the phase of this pushpull output signal in vaccordance with its frequency.

The output terminals of unit I5 are connected to the input terminals of a phase-shift network I'I. `The network Il is constructed to shift 'the phase of -a signal applied thereto by substantially-independent of the frequency of this applied sig-nal within the operating frequency range of the oscillator. The output terminals of the network I'I are connected to the input terminalsof a phase-splitting network I8. One of thecutput terminals of network I8 is connected to thel control-electrode i9 of device lI0 through lalmas-- ing network including a grid-leak Vresistor 2.0 shuntedV by acapacitor 2l. A secondoutput-terminal of network I8 is connected to the control electrode 22 Aof device II through aibiasngmetwork including a grid-leak resistor 23 shunted by acapacitorM. The phase splitting action of network I 8 is substantially independent of frequency within the operating frequency range of the oscillator and this network acts in a manner to be fully described hereinafter, to advance the phase of the signal applied to its input terminals by 45 as applied to control electrode I9, and retard the phase of this signal by 45 as applied to control electrode 22, and thus supply feed-back signals to these control electrodes.

synchronizing pulses are applied to the network I8 by way of terminals 25, these terminals being connected to any suitable synchronizing source (not shown). In a manner to be fully described hereinafter, the synchronizing pulses are translated by the network I8 and impressed in a push-push manner on control electrodes I9, 22 superposed on the feed-back signals supplied thereto through the network I8, the phase of the synchronizing pulses being unaltered by the network I8. The operation of the circuit of Figure 1 may best be understood by reference to Figures 2 and 3. Neglect for the moment the effect o1 the synchronizing pulses applied to terminals 25, and assume that the circuit of Figure l is oscillating at a free-running frequency f substantially equal to the repetition frequency of the synchronizing pulses. The phase-shift network and load impedance I5 is constructed to have a phaseshift versus frequency characteristic as shown in Figure 3. At the free-running frequency f this network preferably imparts zero phase shift to the signal translated thereby. At frequencies below the free-running frequency the phase shift rof this network is leading and at frequencies above the free-running frequency the phase shift is lagging.

The devices I0, II generate individual output signals Epi, Epz and the unit I5 derives from these individual output signals a push-pull output signal represented by the vector Epi--Epz in Figure 2. This output signal is translated by the unit I5 with zero phase shift at the free-running frequency f, and this network produces a signal E1 at its output terminals in phase with the pushpull output signal Epi-Enz, as shown in Figure 2.

The signal Ei is shifted 90 in the network I1 and a signal E2 is produced at the output terminals of this network, the signal E2 being shown in Figure 2 displaced 90 from the signal Ei. The signal E2 is split in the network I8 to produce a signal Egi for application to control electrode I9 leading E2 by 45, and to produce a signal Egz for application to control electrode 22 lagging Ez by 45.

Assume that the load impedance of unit I5 is resistive in nature, then the feedback signals Egi, Egz respectively cause devices I Il, II to produce individual output signals Epz, Epi respectively displaced 180 therefrom. The network I8 produces the signals Egi and Egz of equal amplitude, and these signals bias the devices I0, II equally so that the output signals Epi, Epz are also of equal amplitude. Under these conditions the phase of the push-pull output signal Epi- Epi is as shown in the diagram of Figure 2 and when the parameters of the circuit are such that Egi and Egz have sufficient amplitude, oscillation is sustained in the circuit. Should the anode load impedance not be resistive in nature, it is merely necessary that the network I8 be constructed to impart a proper individual phase relation between the signals Egi, Egz and the signals Epi, Epz so that oscillation may be sustained.

the signal translated thereby and Ei leads or lags Epi- Epz depending upon whether the instantaneous operating frequency is above or below the free-running frequency. Such a phase shift in the signal Ei causes a corresponding phase shift in the signal E2 and, thus, in the signals Egi, Egz

-Thus, in its free-running state the oscillator For frequencies other than the free-running frequency f, the unit I5 imparts a phase shift to reaches a stable operating condition at the frequency f, at which frequency the unit I5 imparts zero phase-shift between the signal Ei and the push-pull output signal Epi-Epi. It would of course be quite feasible to utilize networks II and I8 that impart phase shifts other than the absolute values designated herein, and to provide that the circuit of Figure 1 oscillates in its freerunning state at a frequency at which the unit I5 shifts the phase of the signal Ei relative to the signal Epi-Epz a certain amount to sustain oscillation; the arbitrary values of phase shift utilized in the preceding discussion and the discussion to follow are for purposes of describing the operation of the circuit in a clear and distinct manner.

Reference is now made to Figures 4 and 5. Still neglecting the effect of the synchronizing pulses impressed on terminals 25, the instantaneous feedback signals supplied to the control electrodes I9, 22 by the unit I5 and networks II, I8 are as shown in Figure 4 by the wave forms Egi, Egz. These waves establish an equal grid bias on the devices I0 and I I as indicated by their common alternating current axis, this axis being displaced from the zero axis (above which grid current flows) by an amount determined by the amplitude of the waves Egi, Egz and by the values given the various elements comprising networks 20,2I and 23,24. I

Now, when synchronizing pulses having a repetition frequency substantially equal to the operating frequency f of the oscillator are impressed across the terminals 25, these pulses are supplied to the control electrodes I9, 22 in a push-push manner superposed on the waves Egi, Egz as shown in Figure 5. Due to the phase difference between the waves Egi and Egz, the synchronizing pulses appear superposed on different portions of the respective waves. In the illustrated example, the synchronizing pulses are superposed on the WaveEgz near its positive peak portion, and extend beyond this portion causing the grid bias on control electrode 22 to increase beyond its previous value and the alternating-current axis of the wave Egz to shift in a negative direction. On the other hand, the synchronizing pulses are superposed on the wave Egi in a positive sense near the center of the linear portions of this latter wave and do not extend beyond the positive peak portion of this wave. Therefore, in the illustrated condition the superposed synchronizing pulses do not affect the grid bias on control electrode I9, and the alternating-current axis of the wave Egi remains at its previously establishedposition.

It is apparent, therefore, that the -phase relation between the synchronizing pulses and the -electrode I9.

'the bias on control electrode 22.

legteaoot J5 :waves Egi, Egz Icontrols the relative bias on .the control electrodes I9 .and V22. With the phase relation illustrated 1in Figure 5, the bias on con- 'trol electrode 22 is greater than that oncontrol Should the 'frequency of the .os-

cillator increase, .the synchronizing pulses effectively shiftup the slopes of the waveEgz and Hquency of the oscillator decrease, the lsynchronizing pulses would effectively shift down the slopes of the wave E'gz and up the slopes ofthe rwavelllgl, causing Aa corresponding decrease in A further decrease in frequency of the oscillator would cause the bias on control electrode 22 "to decrease further until the synchronizing pulses no longer extend beyond the positive peak portion of the waves 'Egg and anyA decrease in frequency beyond this point would -then cause the bias on control velectrode 'I9 to increase while the bias on control electrode'22 remains -essentially fixed.

Therefore, any change in frelliency Aof the oscillator circuit f(or of the impressed synchron- 4izing pulses) causes a-corresponding change in "the yrelative biases of devices I0, II depending upon the `direction and magnitude of the frequency change. In accordance with the inof Figure 1, when the-frequency of this circuit -is 'synchronized with synchronizing pulses applied to the terminals 25. It is assumed that the 'repetition frequency of the synchronizing rpulses is slightly lower than the free-running frequency f of the oscillator, Vand the oscillator l'frequency `is synchronized at this slightly lower frequency ywith a phase relation existing between the synchronizing pulses and the feed- 'back'waves Egi, Egz -is as shown in Figure 5.

Therefore, when these synchronizing pulses -are applied to terminals 25, the 'bias of device II increases relative to the 'bias of device Iil, as `previously explained, and the amplitude of the `output signal Epz accordingly decreases relative to the amplitude of the voutput signal Epi Therefore, the push-pull output signal YEpi-E132 derived by the unit I5 shifts in phase from its position in Figure 2 `to the position shown in Figure 6. To re-establish `the proper phase relation between 'the feedback signals Egi, Egz and theroutput Asignals Epi, Epz so that stable oscillation may be sustained, it can be seen from Figure-"3 that the oscillator frequency Vmust decrease fromits free-running vfrequency f to a new frequency atwhich the unit I5 provides a leading vphase relation between the signal El and the `push-pull output signal Epl- E1n required to place feedback signals Egi and Egg back in proper vphase to `sustain stable oscillation. The fre- "quency `of the oscillator circuit is maintained `Vat this synchronized frequency, and any tendency towards frequency drifts away from this A'frequency `is prevented in a manner now to be described.

Should the frequency of the oscillator vtend to Aincrease beyond the repetition frequency of the "synchronizing-pulses, the pulses shift up the slope lof ufthe wave AFez,fand-down the-*slope rof lthe wave 'portion of the curve of Figure 3.

shift `tends to increase further the bias of device IIrelative to the bias of device I', :andthus to decrease further the amplitude of the output signal .Epz .relative to the output signal Epi. This, in turn, causes the vector of .the push-pull output signal Epl- Enz to rotate in a clockwise direction, :andthe frequency of the oscillator `to decrease (inlaccordance with the curve of Figure 3:) so that `the unit I5 may provide the proper increased phase angle to sustain stable oscillation. Thus, any tendency of the oscillator frequency to increase beyond the repetition frequency of the synchronizing pulses sets up a chain of operations that tends to prevent such an increase in frequency. Similarly, should the frequency of the oscillator tend to decrease below the repetition frequency of the synchronizing pulses,.the bias of the device II decreases relative to the bias of device I, increasing theamplitude of the Vsignal Epz relative to Vthe signal Epi. This causes the vector Epi-E112 to rotate in a counterclockwise direction, and the frequency of the oscillator vto increase so that unit I5 may provide a de- .creased phase angle qs to sustain stable oscillation. Thus, any tendency of the oscillator frequency to decrease below the repetition frequency of the synchronizing pulses is similarly prevented. In this manner the synchronizing pulses synchronize the frequency of the oscillator circuit, the synchronizing r-ange being determined by the sloped The slope of the sloping portion of the curveof Figure 3, -in turn, is a function of the quality factor Q of the unit I5 as is well understood in the art.

The circuit of Figure 1 may be considered as a push-pull oscillator of modified type since, unlike usual push-pull oscillators, the feedback components Egi, Egz and the output signals Epi, Epz have a phase relation that is other than This is a requirement of the embodiment of the invention illustrated in Figure 1,-and is necessary in order that changes in the relative amplitudes of Epl and Epz cause a corresponding phase shift in the push-pull output signal Epl-Epe.

Since the synchronizing pulses are applied to the circuit of Figure 1 in push-pull, they cancel in the load impedance portion of unit I5 and do not interfere with the push-pull output signal of the oscillator circuit. Moreover, random noise signals, received concurrently with the synchronizing pulses and impressed on the control electrodes of devices Ie', II charge the capacitors 2I, 24 by substantially equal amounts and have little eiect on the relative amplitudes of the output signals Epl, Epz. Consequently, such noise signals do not interfere materially with the operation of the circuit.

The characteristics of the circuit components of the oscillator of Figure l, and particularly the quality factor of the phase shift network portion of unit I5, are preferably chosen so thatthe Voscillator is highly stable in operation. vFurthermore, it is desirable to construct the oscillator so that its free-running frequency is nearly identical to the repetition frequency of the synchronizing pulses. In this manner, with the oscillator so constructed, it will continue to oscillate at substantially the synchronized frequency even during short intervals when the synchronizing pulses are partially or completely lost in background noise, and synchronism is not destroyed during these intervals.

The-system of Figure 7 includes a unit d designated television receiver,and this receiver contains the Well known radio-frequency amplier, intermediate-frequency ampliiier, video detector and video ampliiier, sound detector and sound amplifier stages utilized in present-day television receivers. The input terminals of the television receiver 4U may be connected to a suitable antenna circuit 4l, and the output terminals of the receiver are connected to the control electrode and cathode of a receiver image tube 42 to control the intensity of the cathode-ray in this tube in accordance with the video-frequency components of a received television signal.

The synchronizing-signal components of the received television signal are separated from the video-signal components in a synchronizing-signal separator 43 having input terminals connected to the receiver 48. The synchronizing signal separator 43 is connected to a vertical deection circuit 44 which, in turn, is connected to the vertical deflection coils 45 of tube 42. The synchronizing signal separator 43 is further connected to a synchronized oscillator and .discharge circuit 46, constructed in accordance with the invention, and the circuit 46 is connected to a usual deflection signal amplifier and coupling stage 41. The output terminals of stage 41 are connected to the horizontal deflection coils 48 of the image reproducing tube 42.

The system of Figure 7, apart from the circuit 46, operates in a conventional manner. Vertical synchronizing pulses from the separator 43 control the operation of the vertical deflection circuit 44 which generates a vertical deflection signal that is synchronized with these vertical synchronizing pulses. This vertical deiiection signal is applied to the deflection coils 45 to control the vertical sweep of the cathode-ray in ldevice 42.

Horizontal synchronizing pulses from the separator 43 are used to control the oscillator 4S which generates a horizontal deflection signal synchronized with these horizontal synchronizing pulses. The horizontal deflection signal is amplified and applied to the deflection coils 43 through the amplifier and coupling stage 41, and this deflection signal controls the horizontal sweep of the cathode-ray in device 42.

Therefore, the cathode ray in device 42 has its intensity modulated in accordance with the video-frequency components of a received television signal, and the sweep of this ray is controlled by the synchronizing-signal components of this television signal. Accordingly, the device 42 reproduces the image represented by the television signal.

One embodiment of the synchronized oscillator of the present invention is illustrated schematically in Figure 8. The circuit of Figure 8 includes a pair of electron-discharge devices G, 6| which may be included, when so desired, in a single envelope. The cathode 62 of device Bil and cathode 63 of device El are connected to ground. The anode 64 of device 6) is coupled to the anode 65 of device 6i through an inductance coil 66. The center tap of coil 66 is connected to the positive terminal B-lof a source oi unidirectional potential whose negative terminal is connected to ground. The coil 63 is shunted by a pair of series-connected capacitors 61, 68 the junction of which is connected to ground, these capacitors forming a tuned circuit with the coil S6.

An inductance coil 69 is inductively coupled to the coil one side of the coil 69 being connected to ground. A series-tuned circuit including a capacitor 13 and inductance coil 1l is connected Y electron-discharge device 14 through a capacitor 15. The control electrode 13 is connected to the cathode 16 of device 14 through a gridleak resistor 11. The cathode 16 is connected to ground through the primary winding of a transformer 18 and through a resistor 19, the resistor 19 being shunted by a capacitor 80. The anode 8l of device 14 is connected to the positive terminal B+ of a source of unidirectional potential through a load resistor 32. The anode 8| may be connected to the amplifier and coupling stage 41 of Figure 7, and is coupled to ground through a series-connected capacitor 83 and variable peaking resistor 84.

A secondary winding 85 of transformer 18 is shunted by a capacitor 86 to form a tuned circuit. The winding 85 is further connected to two terminals of a phase-splitting bridge network comprising resistors 81, 88 and capacitors 89, 90, connected as shown. A third terminal of the phase-splitting network is connected to the control electrode 9| of discharge device 60 through parallel-connected capacitor 92 and grid-leak resistor 93. A fourth terminal of the phase-splitting network is connected to control electrode 94 of discharge device 6I through parallel connected capacitor 95 and grid-leak resistor 96.

Horizontal-synchronizing pulses from the synchronizing signal separator 43 of Figure '1 are applied to the circuit of Figure 8 by way of terminals 91. One of the terminals 91 is connected to ground and the other is coupled to a terminal of the phase-splitting network 81-99 through a capacitor 98, the last-mentioned terminal-of the phase splitting network being connected to ground through a resistor 99.

The circuit of Figure 8 is a schematic representation of the circuit of Figure 1, the additional circuit of discharge device 14 being included therein for purposes to be described. The network 86-68 represents the load impedance and phase shifting unit I5 of Figure 1. This net- Work derives the push-pull output signal Epi- Epe from the oscillator circuit. Furthermore, the network 66-68 is tuned to be resonant at the free-running frequency f of the oscillator and supplies the output signal Ei to the network (iS-12, the signal Ei being in phase with the push-pull output signal Epi--Epz at the freerunning frequency of the oscillator, and leading or lagging the signal Epi- Em when the frequency of the oscillator is below or above this free-running frequency.

The network 69-12 corresponds to the phaseshifting network I1 of Figure 1, and this network is tuned to be series-resonant at the free-running frequency f of the oscillator. The signal E2 may be derived across the capactor 10, this signal leading E1 by 99 at the free-running frequency. As pointed out in the previous discussion, it is required that the phase relation between the signals Ei and Ez remain constantv for frequency variations, and this is substantially the case with the network 69-12 within the operating frequency range of the oscillator. vSlight phase adjustment between the signals E1 and Ez may be made by adjusting the value of the variable resistor 12, included in the series-resonant circuit.

The signal E2 is applied to the control electrode 13 of discharge device 14, this device acting as a discharge tube for capacitor 83 and 9. also as. arr amplitude. stabilizer'for the: signalv E2. Therdevice Iflfis biased to operate' as a` class C amplifier, and current pulses flow in its anode and cathode circuits, iny response to the positive peak portions of the" signal E2V applied to its controly electrode. cathode circuit of the. device flow through the primarywinding of transformer 'I8 and induce a sine-WaveY signal in the tuned circuit 85, 86- this circuit similarly being tuned to the free-running frequency f of the oscillator. pulses are amplitude-limited by theV circuit of device 'I4, so that the. sine/wave in the circuit 85V, 85- has a substantially constant amplitude.

The sine-Wave signal'M from thevtuned circuit 85, 86T isV applied. to thephase-splitting network.

way' of the network 87-90, and superposed on the feed-back signals in the manner previously described.

The signal Ezapplied to the control electrode '|131 of device 'I4causes the device to become conductive-during positivepeak portions of this signal,A since the device is biased to operate as a class- C amplifier. The" device 'I4 additionally acts as a' discharge tube for the capacitor 83, periodically discharging this capacitor and providing a saw-tooth deflection signal for applicationI tothe amplifier stage 41 of Figure '7. The wave sha-peor this deflection signal may be controlled in'` Well-known mannerby adjustment of the variablepeaking resistor 84 connected in series with capaci-tor 83.

As previously pointed out, the oscillator circuit may be constructed to oscillate in a highly stable manner, and even during periods when theE synchronizing pulses are of 10W amplitude and lost in the background noise, the circuit continues to control thev scanning of the receiver reproducing device at substantially the required frequency.. Moreover, as also pointed out, noise or"other vdisturbancesA have no material effect on the synchronization of the oscillator with the received synchronizing pulses. The free-running' frequency' of' the oscillator is made substantially equal to the repetition frequency of the synchronizing pulses and, in the afored'escribed manner, these pulses synchronize the oscillator to theirrepetition frequency.

A second embodiment of the synchronized oscillator of the present invention is illustrated in Figure 9. This latter embodiment includes a pair ofelectron-discharge devices IIB and |II. The cathodes |"|2 and I I3 of devices H0 and III are connected to ground through a resistor H4 shunte'd by'acapacitor |I5. The anode H6 of device III! is connected to the positive terminal B+ ofY a source of unidirectional potential through a parallel-tuned circuit comprising an inductance coil I I'I, capacitor IIB and resistor II9, and tuned to a frequency slightly above the free-running. frequency of the. oscillator circuit. The anode |20 of. device. Il is connected to the The: current pulses in the These current^ 10 positive terminal B+ through aparallel-tuned circuit comprising an inductance coil |2-|, capacitor |22 and resistor |23, and tuned to afrequency displaced below the free-running frequency f of the oscillator an amount equal to the displacement of the frequency to which the rstmentioned parallel-tuned circuit is tuned above the free-running frequency of the oscillator.V For. example, assuming that the free-running frequency f of the oscillator is 16 kc., therstsmentioned circuit may be tuned to 20 kc. and the `last mentioned circuit may be tuned to 12 kc.

A third parallel tuned circuit comprising. inductance coil |24, capacitor |25l and resistor |26 is connected across the above-mentioned two tuned circuits, and this third'circuit is tuned to the free-running frequency of the oscillator so that it is resistive in nature at this frequency and substantially resistive for frequencieswithin. the operating frequency range of the oscillator. An inductance' coil I2'i is inductively coupledto the coil |24, and one extremity of coil |21- is coupled to control electrode |28 of device. I'II through a capacitor I 29, and the other to control electrode I 3@ of device I I0 through a capacitor |3I. The'control electrodes`|28 and |30 are-connected to ground through respective grid-leakresistors |32 and I 33. Incoming'synchronizing pulses may be impressed across terminals |34' connected to the mid-point of coil |21 and to ground.

The operation of the circuit of Figure Q'may best be understood by reference tov Figures 1-0f Figure 10 Ashows vectorially the signal oscillator, and the current 1p1 flowing through'` the device is 180" out of phaserwith the'cur'- rent Ipz owing through devicey I I I. The current' 1p1 gives rise` to an output signal EmV across thel tuned circuit III-I I8, the signal E'pr being displaced in phasel from 1p1 4by an angle 180-'1 due to the fact that this circuit is tuned tol a. frequency above the free-running frequency. j of the oscillator. The current Ipz gives risetoan output signal Epz acrossV the tuned circuit I2I-I-22, signal E132' being displaced. from Ipz an,

fact that this latter circuit is tuned to a corre'- sponding frequency below the free-running; frequency of the oscillator. The push-pull output signal Epi- E112 is in. phase with the currentV Ipzf under these conditions, since EpizEpz and p1- mp2. The signal Epi-Epz appears across the tuned circuit |24-I25 and' is induced into the coil. |21'. Since the extremities of coil |2.'I are coupledv to' the control electrodes |28, |30, an in-phasesignal Egz appears across the resistor |33 and a1l80 out-of-phase signal Egi appears across theresistor |32. It can be seen from the diagram that the signals Egl and Egg are in proper phase to sustain oscillation, and appropriate circuit parameters areused so that E'g1 and Egz have sufficient amplitude to enable the circuit of FigureV 9 to oscillate as a push-pull oscillator at the free*- running frequency f.

Now assume that synclflronizingA pulses havinga repetition frequency slightly lower than the freerunning frequency of the oscillator are impressed across terminals |34. These synchronizing pulses" are supplied to the control electrodes' |28, |3|l in push-push and superposed on they signalsEgr and" Egz, as in the previous embodiment. The devices and Ill are operated in the variable transconductance range 0f their characteristics, so that the application of the synchronizing pulses to the terminals |34 causes the amplitude of the output signal Epz to increase relative to the output signal Epi, in the previously described manner. Now, unless the frequency of the oscillator shifts from a free-running frequency, the push-pull output signal E111-E112 will no longer be in phase with the current Ipz and the feedback signals Egi, Egg will no longer be in proper phase to sustain oscillation. Therefore, the frequency of the oscillator decreases towards the repetition frequency of the synchronizing pulses to establish the signal relations shown in Figure 11. That is, the oscillator frequency decreases to a value wherein the phase displacement 2 of the signal Epz appearing across the low-frequency tuned circuit l2 |-l22 has a decreased value, and the phase displacement 1 of the signal Epi appearing across the high-frequency tuned circuit |||-||8 has an increased value, so that the push-pull output signal Epi-Epe is again in phase with Ipz and oscillation is now sustained in the oscillator at the repetition frequency of the synchronizing pulses. As previously described in conjunction with the first embodiment of the invention, any tendency of the oscillator frequency to drift from this synchronized frequency causes a corresponding change in the relative amplitudes of signals Epi and Epz. This causes a change in phase in the push-pull output signal Epi-Epz and a corresponding shift in frequency of the oscillator to oppose this tendency.

The embodiment of the invention shown in Figure 9 can be constructed to be highly stable in operation, and when the free-running frequency f of the oscillator is made substantially equal to the repetition frequency of the synchronizing pulses, the oscillator continues to oscillate at substantially the synchronized frequency during intervals when the synchronizing pulses are of low amplitude and lost in background noise.

In addition, the synchronizing pulses are applied in push-push to the oscillator of Figure 9 and cancel in the output signal of the oscillator. Random noise signals received concurrently with the synchronizing pulses charge the capacitors |29, |3| by substantially equal amounts so that these noise signals have no material effect on the synchronizing of the oscillator circuit.

The present invention provides, therefore, improved oscillator circuits capable of being synchronizing with received synchronizing pulses without the need for additional synchronizing stages. Moreover, this invention provides improved synchronized oscillator circuits that are highly stable and have a high degree of immunity to noise disturbances and other unwanted signals received concurrently with the synchronizing pulses.

While particular embodiments of the invention have been shown and described modifications may be made and it is intended in the appended claims to cover` all such modifications that fall within the true spirit and scope of the invention.

I claim:

1. A push-pull oscillator circuit to be synchronized with received synchronizing pulses comprising: a pair of electron-discharge devices having individual output electrodes and input electrodes; a first network coupled to said output electrodes of said devices for deriving a pushpull output signal having a phase determined l2 by the relative biases of said devices and for imparting a phase-shift to said output signal that is a function of the frequency of said oscillator;v

a phase-splitting network coupled to said first network for producing two distinct feed-back signals having a phase relation with respect to each other that is substantially independent of the frequency of said oscillator; a biasing network coupled to said phase-splitting network for applying one of said feed-back signals to the input electrodes of one of said devices and the other of said feedback signals to the input electrodes of the other of said devices to sustain oscillation in said oscillator at a frequency dependent on the phase of said output signal; and means for supplying said synchronizing pulses to said biasing network for push-push application to said input electrodes of said devices superposed on said two feed-back signals to control the relative biases of said devices in accordance with the phase relation between said synchronizing pulses and said feedback signals.

2. A push-pull oscillator circuit to be synchronized with received synchronizing pulses comprising: a pair of electron-discharge devices having individual output electrodes and input electrodes; a first network coupled to said output electrodes of said devices for deriving a pushpull output signal having a phase determined by the relative biases of said devices and for imparting a phase-shift to said output signal that is a function of the frequency of said oscillator; a second network coupled t o said first network for shifting the phase of the signal from said first network by substantially a phase-splitting network coupled to said second network for producing two distinct feed-back signals respectively leading and lagging the signal from said second network by predetermined equal amounts substantially independent of the frequency of said oscillator; a biasing network coupled to said phase-splitting network for applying one of said feed-back signals to the input electrodes of one of said devices and the other of said feed-back signals to the input electrodes of the other of said devices to sustain oscillation in said oscillator at a frequency dependent on the phase of said output signal; and means for supplying said synchronizing pulses to said biasing network for push-push application to said input electrodes of said devices superposed on said two feed-back signals to control the relative biases of said devices in accordance with the phase relation between said synchronizing pulses and said feedback signals.

3. A push-pull oscillator circuit to be synchronized with received synchronizing pulses comprising: a pair of electron-discharge devices each including an anode and a control electrode; an output network tuned to they free-running frequency of said oscillator coupled to the anodes of said devices for deriving a push-pull output signal having a phase determined by the relative biases of said devices and for imparting a phase-shift to said output signal of a magnitude and sense dependent on the magnitude and sense of frequency deviations of said oscillator from said free-running frequency; `a series-resonant.

network tuned to said free-running frequency coupled to said output network for deriving av signal substantially in phase quadrature with the signal from said output network for frequencies within the frequency range of said oscillator;

a resistance-capacity phase-splitting network coupled to said series-resonant network for pro.-

ducing two distinct feed-back signals respectively leading and lagging the signal from said seriesresonant network by predetermined equal amounts substantially constant within the frequency range of said oscillator; a biasing network coupled to said phase-splitting network for applying one of said feed-back signals to the control electrode of one of said devices and the other of said feed-back signals to the control electrode of the other of said devices to sustain oscillation in said .oscillator at a frequency dependent on the phase of said output signal; and means for supplying said synchronizing pulses to said biasing network for push-push application to said control electrodes of rsaid devices superposed on said two feed-back signals to control the relative biases of said devices in accordance with the phase relation between said synchronizing pulses and said feed-back signals.

4. A push-pull oscillator circuit to be synchronized with received synchronizing pulses comprising: a pair of electron-discharge devices having individual input electrodes and output electrodes; a rst network coupled to said output electrodes of said devices for deriving a pushpull signal having a phase determined by the relative biases of said devices and for imparting a phase-shift to said signal that is a function of the frequency of said oscillator; a second network coupled to said first network for shifting the phase of the signal from said first network by substantially 90"; a third network coupled to said second network, including an electron discharge device. for obtaining an output signal from said oscillator and for limiting the amplitude of the signal from said second network; a phase-splitting network coupled to said third network for producing two distinct feed-back signals respectively leading and lagging the stabilized signal from said third network by predetermined equal amounts substantially independent of the frequency of said oscillator; a biasing network coupled to said phase-splitting network for applying one of said feed-back signals to the input electrodes of one of said devices and the other of said feed-back signals to the input electrodes of the other of said devices to sustain oscillation in said oscillator at a frequency dependent on the phase of said output signal; and means for supplying said synchronizing pulses to said biasing network for pushpush application to said input electrodes of said devices superposed on said two feed-back signals to control the relative biases of said devices in accordance with the phase relation between said synchronizing pulses and said feedi back signals.

5. A circuit for use in a television receiver for synchronizing the sweep of a cathode-ray image reproducing device with received synchronizing pulses comprising: a pair of electron-discharge devices having individual input electrodes and output electrodes; a rst network coupled to said output electrodes of said devices for deriving a push-pull signal from the circuit of said devices having a phase determinedbyj the relative biases of said devices and for imparting a phase-shift to said signal that is a function of the frequency of said oscillator; a second network coupled to said first network for shifting the phase of the signal from said first network by substantially 90; a third network coupled to said second network, including an electron discharge device, for deriving a sweep signal synchronized with the 14 signal from said second network; means for applying said sweep signal to said image-reproducing device to control the sweep of the cathode-ray therein; a phase-splitting network coupled to said third network for producing two distinct feed-back signals respectively leading and lagging the signal from said second network by predetermined equal amounts substantially independent of the frequency of said oscillator; a biasing network coupled to said phase-splitting network for applying one of said feed-back signals to the input electrodes of one of said devices and the other of said feed-back signals to the input electrodes of the other of said devices to sustain oscillation in said oscillator at a frequency dependent on the phase of said output signal; and means for supplying said synchronizing pulses to said biasing network for pushpush application to said input electrodes of said devices superposed on said two feed-back signals to control the relative biases of said devices in accordance with the phase relation between said synchronizing pulses and said feedback signals.

6. A push-pull oscillator circuit to be synchronized with received synchronizing pulses comprising: a pair of electron-discharge devices having individual output electrodes and input electrodes; a first network, including a pair of resonant circuits tuned respectively to frequencies equally displaced above and below the free-running frequency of said oscillator, for deriving individual output signals from said devices having relative amplitudes dependent upon the relative biases of said devices and for imparting respective phase shifts to said individual output signals determined by the frequency of said oscillator; a second network coupled to said first network for deriving a push-pull signal from said individual signals; a phase-splitting network coupled to said ,second network for producing two distinct feed-back signals displaced in phase by substantially a biasing network coupled to said phase-splitting network for applying one of said feed-back signals to the input electrodes of one of said devices and the other of said feedback signals to the input electrodes cf the other of said devices to sustain oscillation in said oscillator at a frequency dependent on the relative amplitudes of said individual output signals; and means for supplying said synchronizing pulses to said biasing network for push-push application to said input electrodes of said devices superposed on said two feed-back signals to control the relative biases of said devices in accordance with the phase relation between said synchronizing pulses and said feed-back signals.

JACK E. BRIDGES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,867,567 Hansell July 19, 1932 2,079,134 Terman May 4, 1937 2,102,419 Klutke Dec. 14, 1937 2,415,773 Vilkomerson Feb. 11, 1947 2,440,538 Chalberg Apr. 27, 1948 2,444,338 Dimond June 29, 1948 2,471,246 Smith May 24, 1949 

